Virtualization technologies enable computing systems to handle surges of load by provisioning additional virtual machines on an as-needed basis. Hence, instead of over-dimensioning a computing system to handle (potential) peak loads, cloud computing enables these computing systems to acquire and release resources according to their present needs. Scalable systems of this type will hereinafter be referred to as “elastic” systems.
The Session Initiation Protocol (SIP), used for setting up and controlling multimedia communication sessions between end points over a packet-based network such as the Internet, is a stateful protocol. This means that the participants in a protocol exchange have to remember the state of the exchange to adequately respond to protocol incidents. Moreover, the majority of SIP servers are stateful—for instance because they maintain “dialogs” representing the SIP relationship between two SIP User Agents (UAs), which persist for some time. In addition, SIP can run over a variety of transport protocols, including the Transport Control Protocol (TCP), which is itself a state-sensitive protocol.